﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            
            Console.WriteLine("请输入圆的半径");
            string  a = Console.ReadLine();
            double r = double.Parse(a);
            double mianji;
            mianji = r * r * 3.14;
            Console.WriteLine(mianji);
           


        }
       
    }
}
